Apparatus for irradiation in a controlled atmosphere

ABSTRACT

Apparatus which permits treatment of products with ionizing radiation in a controlled atmosphere comprises an inner chamber positioned within an outer chamber, the workpiece to be treated passing through the inner chamber. The outer chamber has a radiation-permeable window in one surface and the second chamber has means for the passage of radiation in juxtaposition with the window in the outer chamber. The apparatus may also contain means for carrying the product to be treated, as well as cooling means at the end of the radiation path.

United States Patent Coleman [451 July 11, 1972 [54] APPARATUS FOR IRRADIATION IN A CONTROLLED ATMOSPHERE [72] Inventor: George E. Coleman, Elmhurst, 111.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Aug. 18, 1969 [211 App], No.: 850,926

[52] US. Cl. ..250/49.5 TE, 250/52, 313/74 [58] Field of Search ..250/49.5 R, 49.5 TE, 5 l 52;

[56] References Cited UNITED STATES PATENTS 2,887,584 5/1959 Nygard ..250/4 9.5TE 3,217,135 11/1965 Eklund ..2l9/l2lEB FOREIGN PATENTS OR APPLICATIONS 1,509,813 12/1967 Francem. ..250/49.5 TE

Primary Examiner-Anthony L. Birch Attorney-Chisholm and Spencer ABSTRACT Apparatus which permits treatment of products with ionizing radiation in a controlled atmosphere comprises an inner chamber positioned within an outer chamber, the workpiece to be treated passing through the inner chamber. The outer chamber has a radiation-permeable window in one surface and the second chamber has means for the passage of radiation in juxtaposition with the window in the outer chamber. The apparatus may also contain means for carrying the product to be treated, as well as cooling means at the end of the radiation path.

15 Claims, 3 Drawing Figures P'A'TE'N'TEDJUL 1 1 I972 INVENTOR GEUPGE COLEMAN v ATTORNEK) APPARATUS FOR IRRADIA'I'ION IN A CONTROLLED ATMOSPHERE BACKGROUND OF THE INVENTION Irradiation of materials to effect curing, sterilization, etc., is known in the art, and processes involving radiation are becoming of increasing importance. The application and curing of coatings is one area in which irradiation processes provide numerous advantages. Irradiation processes are carried out by treating radiation-sensitive materials to high energy radiation and/or the secondary energies resulting from conversion of electrons or other particle energy to X-rays or gamma radiation. While various types of radiation are suitable for this purpose, radiation produced by accelerated high energy electrons has been found to be most economically applicable and to provide generally the most satisfactory results.

Various types of equipment are known to produce radiation, including resonance-type accelerators, electron linacs, Van de Graaff generators, betatrons, syncrotrons, cyclotrons, atomic piles, and others. I

Used in commercial irradiation processes are accelerators operating at energy levels as low as 50,000 electron volts or lower, and as high as million electron volts or even higher. For example, high power electron linear accelerators, such as the ARCO type traveling wave accelerator, Model Mark I, operate at 3 to 10 million electron volts, while commonly used DC type accelerators operate at 100,000 to 4 million electron volts. Such accelerators provide a beam of electrons which can be directed to a given area as desired and thus to the product to be irradiated. Several such accelerators are described in Us. Pat. No. 2,763,609 and British Pat. Specification No. 762,953.

It has been found that the efficiency of irradiation processes in many cases depends upon the environment of the workpiece being irradiated. For example, many materials are more or less radiation-sensitive, depending upon the atmosphere in which they are treated. The presence of certain levels of oxygen in the atmosphere is often a determining factor in both the rate of the desired reaction and the quality of the finished irradiated product. Other factors involve hazards such as the possibility of fire or explosion and the production of ozone during the irradiation process.

It is therefore recognized that it is desirable to carry out irradiation processes in a controlled atmosphere in which the level of oxygen can be maintained within the desired limits. While this is relatively easily carried out in a closed system, most processes cannot be economically performed in closed apparatus and heretofore it has not been possible to provide efficient control of the atmosphere surrounding a workpiece in a process wherein the products treated are continuously or intermittently moving.

One proposal for providing an inert atmosphere during irradiation is described in US. Pat. No. 2,887,584. The apparatus as described therein comprises a chamber open at the bottom into which the product to be irradiated is passed while attempting to maintain a relatively inert atmosphere inside the chamber by use of a lighter-than-air inert gas to displace the air therein. The apparatus as described in the said patent is quite limited in the extent to which oxygen can be excluded from the path of the product to be irradiated, and for this reason does not appear to have been successfully utilized.

SUMMARY OF THE INVENTION The apparatus of the present invention comprises:

A. a first chamber having a radiation-permeable window in a surface thereof,

B. a second chamber positioned within the first chamber and defining a reservoir between the chambers,

C. the second chamber having openings establishing a path of travel for a workpiece and having means for the passage of radiation in juxtaposition with the radiation-permeable window in the first chamber, and

D. means for introducing gas into the path of travel of the workpiece.

The present invention provides apparatus for treating- DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a perspective view of an apparatus comprising one embodiment of the invention. v

FIG. 2 is a longitudinal section through the apparatus shown in FIG. I.

FIG. 3 is a perspective view showing the relationship of the apparatus in conjunction with the lower portion of an electron beam accelerator during use.

Referring to FIG. I, the first or outer chamber 1 has in the top surface thereof a radiation-permeable window 2. A second chamber 3 is positioned within the first chamber and has openings 4 and 4' through which is passing a workpiece 10. The second chamber has an opening 5 for the passage of radiation onto the workpiece. Gas distribution tubes 6 are positioned in the reservoir between the chambers and are connected to a gas source (not shown). Conveyors rolls 7 are located in the bottom of the second chamber and assist in passing the workpiece through the apparatus. Also shown is an auxiliary gas inlet 9 at the inlet opening to the second chamber.

In FIG. 2, the first chamber 1 with the radiation-permeable window 2 contains within it a second chamber 3 having inlet and outlet openings 4 and 4. Another opening 5 in the second chamber is in juxtaposition with the radiation-permeable window. Gas inlet tubes 6 extend transversely through the apparatus and contain a plurality of holes therein for the introduction of gas, the distribution of the gas being shown in the drawing by arrows. Rollers 7 are in the lower surface of the second chamber and cooling tubes 8 provide cooling of the bottom surface of the second chamber in the path of the radiation. At each of the openings in the second chamber, a gas distribution tube 9 is provided, also extending transversely across the opening and having a plurality of holes for the passage of gas.

In FIG. 3, the apparatus comprising the chamber 1 having therein a window 2 is shown in combination with an electron beam accelerator 1], whereby during operation radiation from the accelerator passes through the window 2 ontothe workpiece 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first or outer chamber of the apparatus can be of any suitable size or shape depending upon the nature of the product or workpiece to be treated. It has a radiation-permeable window in one surface, such windows being well known in the art and being formed of a material which substantially excludes the passage of gases, but which permits radiation to pass therethrough. Generally, such windows are made to a section of a metal having a low atomic number, such as aluminum or beryllium, and are usually quite thin, having, for example, a weight of from about 3 to about 10 milligrams per square centimeter. The common aluminum foil of commerce is satisfactory for use as the window. The dimensions of the window and its position in the surface of the chamber are not critical, depending upon factors such as the area scanned by the electron beam, the dimensions of the workpiece, etc.

In some instances, the radiation-permeable window in the chamber can be a common window with the window of the accelerator or other radiation source through which the radiation is emitted. Such an arrangement has the advantage of eliminating one window and thus reduces the loss of radiation occasioned thereby, but also makes the apparatus less flexible and more expensive to repair or replace.

The second or inner chamber is positioned within the first chamber, thereby defining a reservoir between the inner surface of the first chamber and the outer surface of the second chamber. While it is desirable that the second chamber be of a size such that the height above the surface of the workpiece is minimized, its size is also not critical. However, the distance the radiation must travel before meeting the surface of the workpiece affects the distribution of energy in the product treated. The volume of the reservoir thus depends upon the number and type of gas inlets, the flow rate of gas, and the overall dimensions of the components of the apparatus.

The second chamber has openings establishing the path of travel for the workpiece. Ordinarily, these openings are at either end of the second chamber and the path of travel passes through the chamber and beneath the path of the radiation.

The area of these inletand outlet openings should be as low as 1 possible to permit the passage of the workpieces, and the,

larger the area of the inlet and outlet, the longer the path of travel through the second chamber should be. The object is to provide a stable condition inside the second chamber, thereby minimizing differences due to external changes in atmosphere, such as caused by air movements. The dimensions of the openings can be varied depending upon size and shape of the workpiece; the shape of the opening can be regular or irregular as required. Replaceable or movable openings of different configurations can be provided if desired.

The second chamber also has means for the passage of radiation in juxtaposition with the radiation-permeable window in the first chamber. Usually, such means comprise an opening in the surface of the second chamber, aligned with the window in the first chamber. However, there can also be utilized a second radiation-permeable window in the second chamber.

The apparatus also comprises means for the introduction of gas into the path of travel of the workpiece. This is usually accomplished by providing a plurality of gas inlets in the reservoir between the chambers and then providing means for the passage of the gas into the second chamber. Where the second chamber contains an opening for the passage of the radiation, this can serve as one of or the only means for the gas to enter the second chamber. Alternatively, the gas can be introduced into the second chamber, although this is less desirable, or an opening or other passageway can be providedin the second chamber at some point other than the point at which the radiation enters the second chamber.

The number andarrangement of inlets for the introduction of gas and direction of flow of the gas can be varied, and in fact, it has been found that different types of processes require different arrangements. Therefore, it is desirable to provide a plurality of such inlets and that means be provided so that the direction of gas flow can be varied. It is further desirable that these inlets be based at various points throughout the reservoir. Thus, the preferred arrangement is-a series of gas distribution tubes spaced in the reservoir and extending transversely through the apparatus, these gas distribution tubes having a plurality of inlet holes along their length and being rotatable, thus permitting changing the direction of flow. A manifold connected to a gas source is usually employed to provide a uniform gas pressure to each of the gas distribution tubes.

As indicated, the overall size of the apparatus can be varied. The apparatus can be constructed of any material which is not overly sensitive to radiation, i.e., which does not substantially degrade and become unusable when subjected to the type of radiation employed. Most metals, glass, etc., can be used. It is preferred that a noncorrosive material be utilized and stainless steel is the specifically preferred material of construction, except for the radiation-permeable window, which is preferably aluminum.

The apparatus can also be provided with certain optional components. Means for conveying the workpiece along the path of travel can be included, these being, for example, rollers located in the lower portion of the second or inner chamber; these can be power-driven if desired. It is also desirable to include cooling means in the area of the second chamber upon which the radiation impinges when not entirely absorbed by any material being irradiated. Such cooling means can be tubes filled with circulating fluid, a block of heat-conducting material, a water or other reservoir, or any other means which pemtits absorption and/or transfer of heat.

Other auxiliary equipment which is often desirable include means for introducing gas at the inlet and outlet; these can be gas distribution tubes similar to those located in the reservoir, placed above the opening with gas flow directed downward, preferably at 45 angle. Still other optional features include provision for continuously or periodically analyzing the atmosphere inside the chamber, means for viewing the workpiece, such as cameras, etc., vacuum or other pumps, and the like.

The apparatus can be varied in structure to meet the needs of specific processes in which it is employed. For example, the apparatus can be used in conjunction with more than one source of radiation, by providing a plurality of radiationpermeable windows as required. For example, both sides of a workpiece can be irradiated or a workpiece of complex shape can be irradiated from various angles.

In one embodiment of the invention, an apparatus as shown in the drawings comprises a first or outer chamber 24 inches long, 54 inches wide and 6% inches deep, having in the top surface a radiation-permeable window made of aluminum 0.7 mils thick) and 50 inches wide and 5 inches long. The second or inner chamber is 36 inches long, 50 inches wide and 1 )4 inches deep. Each of the inlet and outlet openings in the second chamber is 50 inches wide by 1 34 inches high, and the second chamber also contains an opening for the passage. of radiation which is 50 inches wide and 10 inches long and is aligned immediately under the radiation-permeable window. Eight gas distribution tubes positioned above and below the second chamber in the reservoir area extend transversely through the apparatus;.the tubes are rotatable and each tube has 53 holes therein, each'hole being 0.090 inch in diameter. The tubes are connected to a manifold which is in turn connected to a source of nitrogen. A conveyor is used to pass the workpiece through the second chamber with three powerdriven rollers in the bottom of the second chamber aiding in the passage.

The apparatus as described is constructed of stain-less steel and can accommodate workpieces up to about 48 inches wide and about three-quarters inch thick.

In operation of the above-described apparatus, a total nitrogen flow of 45 cubic feet per minute is passed through the manifold and distributed by the gas distribution tubes in the reservoir. A product line is carried through the second chamber at a rate of 35 feet per minute. During such operation, the concentration of oxygen in the path of travel of the workpiece is less than parts per million. By reducing the speed of travel and/or the size of the product line, the oxygen content can be reduced to below 60 parts per million.

The apparatus can also be used to provide a sustained level of oxygen (or other gas) during operation. This is desirable using some coating materials, for example, and is accomplished by feeding a controlled mixture of oxygen and nitrogen through the gas distribution system. An advantage of the use of the apparatus in this manner is that ozone and other gaseous by-products are removed during operation and thus the concentration of such by-products does not build up to undesirably high levels. The apparatus can also be operated at reduced pressure, by providing suitable auxiliary equipment, e.g. pumps, chambers, etc.

According to the provisions of the patent statutes, there are described above the invention and what are now considered to be its best embodiments. However, within the scope of the appended claims, it is to be understood that the invention can be practiced otherwise than as specifically described.

I claim:

1. In an apparatus for treating products with ionizing radiation in a controlled atmosphere A. a first chamber having a radiation-permeable window in a surface thereof,

B. a second chamber positioned within said first chamber and defining a reservoir between said chambers,

C. said second chamber having spaced inlet and outlet openings for a workpiece establishing a path of travel for v said workpiece and having means for the passage of radiation in juxtaposition with said radiation-permeable window,

D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings, and

E. means for introducing gas into said path of travel.

2. The apparatus of claim 1 in which said second chamber extends through said first chamber.

3. The apparatus of claim 1 in which said means for introducing gas comprises means for introducing gas into said reservoir.

4. The apparatus of claim 1 in which said means for the passage of radiation in said second chamber is an opening in one surface of said chamber.

5. In an apparatus for treating products with ionizing radiation in a controlled atmosphere A. a first chamber having a radiation-penneable window in a surface thereof,

B. a second chamber positioned within and extending through said first chamber and defining a reservoir between said chambers,

C. said second chamber having spaced inlet and outlet openings establishing a path of travel for a workpiece and having an opening for the passage of radiation in juxtaposition with said radiation-permeable window,

D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings, and

E. means for introducing gas into the reservoir between said first chamber and said second chamber.

6. The apparatus of claim 5 in which cooling means is provided in a portion of the surface of said second chamber.

7. The apparatus of claim 5 in which said means for introducing gas comprises a plurality of gas distribution tubes.

8. The apparatus of claim 5 in which additional means for the introduction of gas are provided at the said inlet and outlet openings in said second chamber.

9. The apparatus of claim 5 in which means for conveying the workpiece along said path of travel is provided in the lower surface of said second chamber.

10. The apparatus of claim 9 in which said means for conveying the workpiece comprises rollers.

l 1. In an apparatus for treating products with ionizing radiation in a controlled atmosphere a A. a first chamber having a radiation-permeable window in a surface thereof,

B. a second chamber positioned withinsaid first chamber and defining a reservoir between said chambers,

C. said second chamber having spaced inlet and outlet openings for a workpiece establishing a path of travel for said workpiece and having means for the passage of radiation in juxtaposition with said radiation-permeable window,

D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings,

E. means for introducing gas into the path of travel into the path of travel of said workpiece, and

F. means for passing ionizing radiation through said radiation-permeable window into said path of travel.

12. The apparatus of claim 11 in which said means for passin ionizing radiation is an electron beam accelerator.

13. e apparatus of claim 12 in which said accelerator comprises a radiation-permeable window which is a common window with the radiation-permeable window in said first chamber.

14. The apparatus of claim 12 in which said accelerator is an electron linear accelerator operating between about 3 million and about 10 million electron volts.

15. The apparatus of claim 12 in which said accelerator is a DC accelerator operating between about 100,000 and about 4 million electron volts. 

1. In an apparatus for treating products with ionizing radiation in a controlled atmosphere A. a first chamber having a radiation-permeable window in a surface thereof, B. a second chamber positioned within said first chamber and defining a reservoir between said chambers, C. said second chamber having spaced inlet and outlet openings for a workpiece establishing a path of travel for said workpiece and having means for the passage of radiation in juxtaposition with said radiation-permeable window, D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings, and E. means for introducing gas into said path of travel.
 2. The apparatus of claim 1 in which said second chamber extends through said first chamber.
 3. The apparatus of claim 1 in which said means for introducing gas comprises means for introducing gas into said reservoir.
 4. The apparatus of claim 1 in which said means for the passage of radiation in said second chamber is an opening in one surface of said chamber.
 5. In an apparatus for treating products with ionizing radiation in a controlled atmosphere A. a first chamber having a radiation-permeable window in a surface thereof, B. a second chamber positioned within and extending through said first chamber and defining a reservoir between said chambers, C. said second chamber having spaced inlet and outlet openings establishing a path of travel for a workpiece and having an opening for the passage of radiation in juxtaposition with said radiation-permeable window, D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings, and E. means for introducing gas into the reservoir between said first chamber and said second chamber.
 6. The apparatus of claim 5 in which cooling means is provided in a portion of the surface of said second chamber.
 7. The apparatus of claim 5 in which said means for introducing gas comprises a plurality of gas distribution tubes.
 8. The apparatus of claim 5 in which additional means for the introduction of gas are provided at the said inlet and outlet openings in said second chamber.
 9. The apparatus of claim 5 in which means for conveying the workpiece along said path of travel is provided in the lower surface of said second chamber.
 10. The apparatus of claim 9 in which said means for conveying the workpiece comprises rollers.
 11. In an apparatus for treating products with ionizing radiation in a controlled atmosphere A. a first chamber having a radiation-permeable window in a surface thereof, B. a second chamber positioned within said first chamber and defining a reservoir between said chambers, C. said second chamber having spaced inlet and outlet openings for a workpiece establishing a path of travel for said workpiece and having means for the passage of radiation in juxtaposition with said radiation-permeable window, D. said first and second chambers substantially completely enclosing said path of travel between said inlet and outlet openings, E. means for introducing gas into the path of travel into the path of travel of said workpiece, and F. means for passing ionizing radiation through said radiation-permeable window into said path of travel.
 12. The apparatus of claim 11 in which said means for passing ionizing radiation is an electron beam accelerator.
 13. The apparatus of claim 12 in which said accelerator comprises a radiation-permeable window which is a common window with the radiation-permeable window in said first chamber.
 14. The apparatus of claim 12 in which said accelerator is an electron linear accelerator operating between about 3 million and about 10 million electron volts.
 15. The apparatus of claim 12 in which said accelerator is a DC accelerator operating between about 100,000 and about 4 million electron volts. 